Physically paging through a large paper document is a process well-known to individuals. One generally twists the edge of the document, allowing the thumb to let the pages freely open in sequence. Depending on the twisting and thumb force applied, the pages either open slowly or quickly. One can quickly move to any spot in the document this way, and see each page in order at whatever speed is desired. There are no limits to the speed used, other than one's own ability to process information. If someone has made an annotation on a page of that paper document, in an ink of contrasting color, the annotations are often easy to see and find even when casually flipping through the document at very high speed.
In the electronic arena, the electronic analogue to flipping pages of a document is scrolling of documents using some type of scroll bar, which is well known in the art. For example, one usually acquires control of a thumb bar using a pointing device (e.g., a mouse). When the thumb bar is moved, pages from the document are displayed by choosing the page that correlates to the current thumb bar position and displaying it. Once the display of one page is complete, the process is repeated. If the thumb bar is moved slowly enough, then every page can be seen. Typically, though, if the thumb bar is traversed quickly, only a small subset of the pages is displayed. There are alternatives to these electronic systems. Some allow the user to view an array of page thumbnails. Such systems work well for a small number of pages, but scale poorly for large documents.
Clearly, for navigating by visual appearance and recognition, the current electronic systems are vastly inferior to the physical process. One can easily miss important pages, and one gains little sense of the document's contents or structure during the navigation process.
Of course, there are many problems that prevent electronic systems from emulating the experience of paper. One key problem is “display refresh rate.” The hardware display system of an electronic device repaints its image at some fixed rate. A typical computer display can only refresh about 60-80 times per second. This constitutes an upper limit on how frequently the image on a display device can be changed.
Furthermore, in order to render any image on a display device, some (usually software) component of the system must arrange to place the image in the device's “display buffer.” If the image must be retrieved from a disk or composed on the fly from some symbolic format, it may take longer to produce and place in the display buffer than the refresh rate of the display. This “system frame rate” may impose another, more stringent, limit on the speed at which a display device can show a series of images.
Thus, both the display rate and the system frame rate seem to impose limits on how rapidly a user can scan through a document without “skipping” some of its pages. This is, indeed, how a DVD player or VCR plays faster than its standard speed, by skipping many frames. But skipping pages in a document a user is scanning through is a very bad idea, since one is likely to miss the feature for which the search is being performed.
The VCR, DVR, or DVD system, or, somewhat more remotely, an audio tape or CD audio system, allows performing a fast forward operation. Most such systems simply stop where they are when the user tells them to stop. There are Tivo systems that do make an effort to jump back to the point at which the user wanted to stop. Since these systems allow fast-forwarding at different speeds, they do jump back different amounts depending on the speed at which they had been running forward.
There are systems that perform a fast forward operation that automatically stops. An example of such a system is a television program playback system. In a television program playback system, when to stop scanning forward to skip commercial advertisements is controlled by changes in chroma balance, which signal the end of a commercial and the resumption of the desired program material.
Image-based document analysis systems perform similar functions. In this field, systems analyze images to find patterns and try to infer structure. Such inferred structure can then be used to aid navigation or to help users find images or documents of interest. Feature-oriented systems exist that help users recognize previously seen documents or images by refining search.
The problem of aiding navigation by providing the user of a page- or image-oriented system some kind of information to help orient the individual as to where the current focus is within the surrounding context is not new. Indeed much work has been done on such “focus and context” supporting systems within the Human-Computer Interaction research and development communities. But such systems perform this function by displaying some kind of overview within which the user can understand the context of the focused page or image.
Information visualization systems discover similarities in underlying data and try to present them visually in such a way that the user (rather than the system) can distinguish patterns or interesting phenomena.